Human G-CSF is a hematopoietic factor found as a differentiation-inducing factor for hematopoietic stem cells of the granulocytic lineage and is clinically used as a therapeutic agent for neutropenia following bone marrow transplantation or cancer chemotherapy because it promotes in vivo hematopoiesis of neutrophils. In addition to this action, human G-CSF acts on stem cells to stimulate their differentiation and proliferation, and also recruits stem cells from the bone marrow into the peripheral blood. Based on the latter action, in fact, transplantation of the peripheral blood hematopoietic stem cells recruited by human G-CSF, i.e., peripheral blood stem cell transplantation is performed in a clinical setting, with the aim of facilitating hematopoietic recovery in cancer patients after intensive chemotherapy.